The present invention generally relates to the production of expanded polystyrene foam articles, and more particularly to the use of waste (used) expanded polystyrene foam materials in the production of new expanded polystyrene foam articles.
Expanded polystyrene foam is used throughout the world for a variety of different purposes. Many different manufacturers produce expanded polystyrene foam and products made from it, including but not limited to the Dow Chemical Company of Midland, Mich. which sells thermo-formed expanded polystyrene foam under the registered trademark STYROFOAM. Exemplary uses for expanded polystyrene foam include but are not limited to shock-absorbant packing materials, insulation materials for buildings, drinking cups, insulated containers, and the like. Expanded polystyrene foam products are strong, light, durable, and have excellent insulating properties. Various references involving the production of polystyrene foam include U.S. Pat. Nos. 2,797,443 and 3,072,584 which are incorporated herein by reference. Additional information on polystyrene foam is provided on pages 97-98, 271-272, 296, and 314-315 of the Modern Plastics Encyclopedia, Vol. 49, No. 10A (1972-1973) which is also incorporated herein by reference.
The production of expanded polystyrene foam conventionally begins with styrene monomer materials which are derived from crude oil. The styrene monomers are polymerized within a water suspension through the use of a free-radical initiator composition known in the art (e.g. an organic peroxide or persulfate). The polymerization process is exothermic in nature, and produces approximately 290 BTU/lb. of styrene monomer. In order to facilitate the polymerization process, various additional materials may be added to the water/monomer suspension, including but not limited to surfactants and the like. The resulting product consists of small beads having an average diameter ranging from about 0.0083-0.079 inches.
The beads are then impregnated with a material known as a "blowing agent" which enables subsequent expansion of the beads to occur. A preferred blowing agent consists of pentane. To impregnate the blowing agent into the beads, they are first introduced into a continuously-agitated pressurization vessel. Again, water, surfactants, and other additives known in the art may be added to the vessel along with the beads. The blowing agent is then introduced into the vessel, with the blowing agent thereafter impregnating the beads through various voids and pores in the bead structure. The beads are subsequently dried and sized as desired (preferably using a vibrating screen-type mechanism known in the art). Completed beads having a blowing agent (e.g. pentane gas) impregnated therein are commercially available from a wide variety of sources, including but not limited to Arco Chemical Company of Philadelphia, Pa.
The beads are then expanded using heat (e.g. steam) in a conventional manner to achieve a desired size and density. In a preferred embodiment, the completed beads at this stage have an average density of about 1.0-1.5 lb./cu. ft. Following expansion and stabilization (e.g. storage of the beads to allow the outgassing of residual pentane and moisture therefrom), the beads are placed in a mold which is used to produce the desired expanded polystyrene foam articles using heat and applied pressure.
However, in recent years, a number of environmental concerns have been raised with respect to expanded polystyrene foam articles. Specifically, expanded polystyrene foam is highly resistant to normal biodegradation processes, potentially causing disposal problems. Because expanded polystyrene foam does not degrade, it occupies a substantial and inordinate amount of space in landfills and waste storage sites. Many cities, states, and countries have imposed restrictions on the use of expanded polystyrene foam products, and have implemented rules stating that packaging products must have a specified amount of recycled/recovered materials therein. For example, the city of Portland, Ore. USA passed an ordinance banning the use of polystyrene foam food containers and the like in view of numerous disposal problems with respect to these materials. In addition, Germany recently imposed a new recycling law that requires the recovery of at least 50% of all packaging materials by January 1993, and further requires the recovery of at least 80% of all metal, plastic, glass, and paper packaging materials by mid-1995.
With respect to expanded polystyrene foam, a number of methods have been attempted in order to recycle/recover this material. For example, waste foam materials have been ground and combined with virgin foam beads, with the waste foam materials merely functioning as "filler". This method is relatively ineffective, since waste foam materials have no fusion properties. As a result, the molded, expanded polystyrene product produced using this technique will have an inconsistent appearance and will fracture more easily on impact compared with virgin expanded polystyrene foam materials. Another technique involves the application of relatively high heat to waste polystyrene foam so that the foam melts as described in U.S. Pat. No. 4,136,142 to Hargreaves et al. This process produces sheets of a material known as "high impact polystyrene" which has a number of undesirable physical properties/weaknesses. In addition, this is considered a "lower" form of recycling since the original structural and functional characteristics of the expanded polystyrene foam are lost with respect to the recycled product.
Thus, a need remains for a method wherein waste expanded polystyrene foam materials may be recycled in an effective, cost-efficient, and environmentally sound manner. The present invention satisfies this need in a unique and beneficial manner as described below.